Spark plug



E. R; HOLMES Jul 16, 1940.

SPARK PLUG EiledjNOv. 6) 1939 IN V EN TOR.

8 a r 5 k/ II 3 "MW 4 4 4 Jib/mks FIG.

A TTORNEYS.

FIG-3 Patented July 16, 1940 UNITED STATES SPARK PLUG Edgar R. Holmes, Denver, 0010., assignor to Holmes Induction Devices, Inc'., Denver, 0010., a corporation of Colorado A Application November 6, 1939, Serial No. 303,060 7 Claims. (011123-169) This invention relates to improvements in ignition devices and has reference more particularlyto an ignition device of the type employed in connection with internal combustion engines and popularly referred to as spark plugs.

It is well understood that the efliciency of a spark plug or ignition device depends upon the character of the spark produced thereby. If a big intense spark is produced, the ignition will 19 be initiated with greater force and the resultant combustion of the gaseswill take place more quickly and be effected more thoroughly than if the ignition was started by means of a weak spark.

It is the object of this invention to produice a spark plug of a simple and substantial construction that shall embody a new combination of elements and structures by means of which an intense spark will be produced when such a plug is substituted in an "ordinary ignition circuit for the spark plugs now in common use.

Another object of this invention is to produce a spark of such construction that the magnetic effect of the electric current is taken advantage of for the purpose of intensifying and prolonging the spark.

A still further object is to produce a spark plug in which a condenser effect is'provided that tends to effect an accumulation of electricity which will be suddenly released with the result that the spark will have greater volume than ordinarily.

It 1st commonly accepted that high tension currents produced by an inductive action are highly oscillatory in character and therefore in accordance with ,the well known theory commonly referred to as skin effect such currents travel primarily along the outer surface of the A conductor provided for their guidance.

It is also well understood and accepted that an electric current traveling through-a conductor will set up magnetic lines of force that travel around the conductor in a clockwise direction when viewed in the direction in which the current travels. When such a current travels in a helical path, these lines of force combine and form a magnetic field of an intensity corresponding to the number of turns and the value of the current. This principle, is taken advantage 5 .of in the production of electric magnets, transformers and other inductive apparatus.

An electric current will travel along the path of least resistance and therefore if the conductor through which the current is passing has paths M of various resistance, the current will be divided ,value of the resistance.

The spark plug or' ignition device which forms the subject of this invention is constructed in such a manner that advantage is taken of the 5 above characteristics of an electric currentand in such a way that these characteristics are made to produce a spark of greater intensity than that normally obtained.

In order to explain the invention in such a way 10 that it can be readily understood, reference will now be had to the accompanying drawing in which the invention has been illustrated in a spark plug and in which:

Figure 1 is a side elevation of a spark plug con- 16 structed in accordance with this invention;

Figure 2 is a longitudinal, diametrical section through the spark plug shown in Figure 1;

Figure 3 is a bottom plan view looking in the direction of arrow 3, in Figure 2;

Figure 4 is a perspective view of the spark gap electrodes; and I Figure 5 is a fragmentary section showing the distri, ution of the magnetic lines of force.

In the drawing reference numeral 6 represents a body member of insulating material preferably made from sillimanite. The lowerend of this body is provided with a threaded portion 1 of somewhat smaller diameter [than the part directly above, which has been designated by ref- 0 erence numeral 8. A shoulder 9 is formed between the sections of diiferent diameter; that portion of the insulating body above the shoulder 9 has been shown as of circular cross section and gracefully curved so as to give a pleasing appear- 35 ance. The lower end of the threaded section terminates in the cylindrical tubular member Ill.

The insulating body 6 has an opening extending longitudinally throughout. The upper portion of this opening is provided with coarse threads 40 II and terminates in an inclined shoulder I2 which joins the threaded section with the cylindrical opening l3 that extends downwardly through the part designatedby numeral I0. A central electrode ll which ismade of some highly a; refractory material, such as Nichrome is attached at its upper end to a short metal section l5 whose outer surface is threaded so as to cooperatelwith the threaded opening II. A layer of cement l6 surrounds the electrode and posi- 5o tions ,it firmlyin the insulating member. The upper end of electrode has a cylindrical opening in which is positioned a metal plug ll of nonmagnetic material, such, for example, as copper. The electrode preferably has a pressed fit 7;"; aaoaoso with the opening in member It so that the two form an assembly that can be readily handled during the manufacture of the plug. A metal base I8, which may be made of steel or of any other. suitable material, is provided with a central opening of different diameters. The upper portion of the opening in base it is internally threaded so as to cooperate with the thread i on the insulating body 6. The threaded opening in the base l8 terminates ina downwardly inclined shdulder it that is positioned a short distance below the inclined shoulder 28 of the insu-' luating body and the space formed between the two is filled with a suitable cement 2 l The upper end of the opening in base it has an enlarged portion 22 that is also filled with a suitable cement 23. After the insulating body has been threaded into the base and the cement hardens,

the two parts form a nonseparable assembly which is sealed against leakage. The lower end of the base terminates in a tubular threaded section 25 that is provided with a downwardly flaring opening; a metal electrode 25 is positioned n a groove 26 on the inside of the tubular member 26. This electrode has been shown in perspective in Figure 4 and in plane view in Figure 3 and from these figures it can be seen that it is provided with four inwardly extending arms 2? that terminate a short distance from the outer surface of the electrode It. This construction provides four spark gaps in parallel. A gasket 28 is positioned beneath the shoulder 29 of the base to form a seal between this shoulder and the engine block. Threadedly connected with the upper end of the opening in the insulating body is a tubular electrode 30. This electrode has a portion 3i of somewhat larger diameter and which forms a shoulder 32 at the place where it'connects with the threaded section 3c. The .upper end of the opening in theinsulating memher is of increased diameter as indicated at 33 and the space thus formed is filled with a cement 36; above the knurled section 3! there is a neck 35 of somewhat smaller diameter that terminates in a head 36 which is provided with an annular groove 37. The tubular conductor terminates at a point indicated by reference numeral 38. It will be noted that the inner surface of the tubular conductor is provided with threads 1-39 of fine pitch whose function will hereinafter V .be explained. Positioned in the upper end of the which is afforded by the core li. upper end of core tit is positioned in the insuopening in the tubular conductor is a tubular in sulating member it into which the upper end of a core ill of magnetic material projects. The lower end of the opening in the tubular conductor 38 has a smooth inner surface and positioned in this is a tubular sleeve 62 whose lower end is provided with a head of somewhat larger diameter which serves as a means for limiting the inward movement of' the sleeve. The opening in sleeve 32 is slightly-larger than the diameter of the core li which therefore can move freely therein. The lower end of thecore 66 is tapered so as to form a conical surface in thezmanher indicated by reference numeral t3 and the point of this rests on the plug I? which, in the embodiment shown, has a conical depression for the reception of the conical point 38. It will be observed that the tubular conductor terminates a short distance above the part it and that the lower end of the sleeve 52 also terminates above this part and therefore there is no direct elec-- trical connection between the two except that Since the lating cap M3 and held in axial alignment with the opening in the tubular conductor and since the point $8 is centered by the action of the conical surface on which it rests, this core is not electrically connected with the tubular conductor, but is separated therefrom by a gap 66 which is the distance between the inner wall pression during the assembly of the plug.

Let us now assume that the tubular electrode at is connected to the secondary of a hightension transformer which has been designated by reference numeral 65 whose outer terminal is grounded. A high tensioned current will now flow downwardly through the tubular conductor and across the spark gap at, thence downwardly through the electrode l6 and across the spark gaps provided between it and the electrodes 21. Due to the fact that the tubular electrode is quite thin and to the further fact that the threads on the outside are coarse, the path of least re-' sistance will be along the threads and therefore some of the current will travel helically around this electrode. If the current was direct and of a low tension, there would be a considerable portion traveling in a straight line, but due to the high tension above referred to, a greater proportion of the high tension current will follow the threads with the result that an effect will be produced substantially as if the current were passing through a helix. This helical flow of the 'current'produces a self-induction which resembles that obtained by an ordinary induction coil and this induction, as is well known, first tends to retard the flow of the alternating cur-' rent and then tends to keep it flowing in the direction iniwhich it is flowing and on reversal an inductive kick is produced which serves to intensify thespark. The fine threads on the inside act somewhat as a secondary winding where high tension alternating current is employed. However, the principal effect is believed to be due to the helical travel of the current inthe coarse threads on the outside. The inductive eflect is greatly-enhanced by the presence of the spark gap. The efiect of the auxiliary spark gal is obtained here by spacing the core til away from the inside of the sleeve.

In Figure a diagram has been shown in which the path of the alternating current has been designated by a dot and dash line 66, the path of the magnetic flux being indicated bylines designated by reference numeral 37. The arrow point 53 shows the place where the current Particular attention is called to the importance of the core of magnetic material as the effect of the magnetizing action of the current is greatjumps from the tubular conductor to the core ly increased by the presence of a soft iron core. It is possible to substitute for the soft iron a permanent magnet, but due to the permanency of the magnetism, the action is asymmetrical 5 and it is believed that the symmetrical effect produced by a soft iron core is superior, although the permanent magnet has a beneficial eflect over that obtained if a nonmagnetic core were used. Lo Comparative tests extending over a considerable length of time have shown that the igni-' tion obtained by means. of spark plugs constructed in the manner above described is far superior tothat obtained with the ordinary spark plugs id and in many cases this effect is so marked as to be readily apparent to any one driving the automobile thus equipped It is evident that the threads can be made deeper than shown on the drawing and that the to root portions can be closer to the inner surface of the tube so as to make the helical travel of the current more pronounced with the frequencies below those resulting in skin effect. The pitch of the threads and their depth, as illusas trated on the drawing, are merely for the purpose of explaining the construction and operation and are not intended to be considered as indicating the exact scale as it is evident that variations in pitch and depth can be made so ID as to obtain the best results.

Having described the invention what is claim as new is:

1. A spark plug central electrode formed from two spaced sections, one of which is tubular, a

w core of magnetic material in the tubular section,

the core being of smaller diameter than the opening in the tubular section, an insulator separating the magnetic core from'the tubular electrode section, one end of the core being in electrical a contact with the other electrode section. I

' 2. An electrode for a high tension spark gap comprising a tubular electrode whose outer surface is provided with a coarse helical thread on its outer surface, a core of conducting material in the electrode, the core being smaller than the opening in the electrode and an insulator separating the core electrically from the electrode.

3. A center electrode for use in a spark plug comprising two electrode sections adapted to be assembled maligned position in an insulatin body, said sections being spaced apart, one of said sections being tubular and provided on its outer surface with a coarse thread, an iron core positioned in the tubular section, the core being other, one of which is tubular, a ridge of elec-- trical conductive material extending helically around the tubular section, said ridge being positioned in the helical groove, a core of magnetic of smaller cross section than the opening in the material in the tubular electrode, the core being of smallerdiameter than the electrode, means comprising an-insulator for centering the core in the electrode and for spacing it therefrom, the core having one end in electrical contact with the other electrode section;

"'5: In a spark plug having a tubular base of conducting material provided at one end with a threaded outer surface for effecting a connection with an engine, and a tubular body of insulating material having one end positioned in the base and secured thereto,.a portion of the wall of the opening in the tubular insulating member having a coarse helical thread, a central electrode formed from two spaced sections positioned in the insulating member, one of said sections being tubular and provided on its outer surface with a coarse helical thread for engagement with the threads in theinsulating body, a core of soft iron positioned in the tubular electrode section, the core being of smaller diameter than the opening in the tubular electrode section, means comprising an insulator for centering the core in the opening, in the tubular electrode section and for insulating it therefrom whereby a spark gap is formed, one end of the core being in electrical contact with the other other end being threaded, a tubular body of insulating material adapted to be positioned in the tubular base, the outer surface of said body being threaded for engagement with the threads in the base, the insulating body having a central opening of different diameters, the lower end being smaller than the upper end, the wall of the larger section of the opening being provided with coarse threads, a central electrode formed from two separate parts, positioned in the opening in the insulating bodypthe lower part extending through the opening of smaller diameter,

the upper section of the electrode being tubular and provided on its outer surface with threads for engaging with thethreaded wall 01 the insulating body, the adjacent ends of the electrode sections being spaced apart, a core of magnetic material of high permeability positioned in the tubular electrode section with one end'contacting the-other electrode sections, the core being smaller than the opening in the tubular electrode section, and means comprising an insulator for centering the core therein and for insulating it therefrom whereby a spark gap is formed.

7. Aspark plug central electrode formed from two spaced sections, one of which is tubular, a

core of conducting material in the tubular section, the core being of smaller diameter than the opening in the tubular section, an insulator separating'the conductive core from the tubular electrode section, one end of the core being in electrical contact with the other electrode section. c

- EDGAR R. HOIMEd. 

